One technique for forming stacked integrated circuit (IC) device is stacking a first wafer having a plurality of IC dice on a second wafer having a plurality of IC dice. The stacked wafers are cut to separate the stacked IC devices, wherein the stacked IC devices includes at least one die from the dice formed on each wafer.
During the stacking process, electrostatic discharge (ESD) between the wafers will often damage one of more of the dice, thereby reducing the stacked IC device yield. In order to mitigate ESD, ionized air is typically utilized to discharge the wafers before stacking. However, ionized air often does not completely remove the charge from the wafer, and often concentrates the charge in isolated regions of the wafer, so when the wafers are stacked, the EDS from these isolated regions having concentrated charge actually increases the number of damaged dice. Since the damage occurs late in the fabrication process, the cost due to the damaged dice and consequently the reduced stacked IC device yield is undesirably high.
Therefore, there is a need for improved techniques for wafer to wafer stacking of integrated circuit chips (e.g., dice) to form stacked IC devices.